When the body is injured, damage to the vascular vessels results in the loss of blood from the vasculature. To prevent continued blood loss, the body stops this flow of blood by means of haemostasis, which causes the formation of a blood clot or thrombosis.
Whilst blood clotting is essential for the repair of wounds, thrombosis can occur anywhere within the circulatory system. As such, thrombosis is a major cause of death due to restricted blood flow to vital organs. A thrombosis which forms within the blood vessels of the heart, lungs, brain or limbs can be particularly life threatening, causing conditions such as heart attack, stroke and deep vein thrombosis. Individuals who have undergone surgery, suffer from heart disease or who are at risk of thrombosis, are prescribed drugs such as the anti-coagulant Warfarin, to prevent unwanted thrombosis formation within blood vessels. Such medications are highly potent with long-lasting effects. For example, the drug Warfarin has a half-life in the body of around 2.5 days. Overlap between maintenance doses and the effects of lifestyle and other medications mean that efficient monitoring is critical to enable management of the dosage of anti-coagulant drugs. The administration of too much anti-coagulant medication can cause haemorrhaging, whilst too little can result in the formation of unwanted clotting.
There are a number of clinical tests that are used to routinely determine the level of anti-coagulant agents present in a blood sample. Of these, one of the most common is the prothrombin time (PT) test. The PT test measures the time taken for a sample of blood to clot in the presence of a clotting agent such as Thromboplastin and calcium. The amount of anti-coagulant present in a sample can be determined as it is inversely proportional to the clotting time. Differences in the type of Thromboplastin administered leads to variations in results between different equipment manufacturers and laboratories when performing the PT test. To overcome this, the medical field has adopted the Internationalised Normalised Ratio (INR) to express PT.
Another test used to determine the level of anti-coagulant agents present in a blood sample is the Activated Partial Thromboplastin Test (APTT). In this test, a sample of plasma is tested by adding phospholipids, an activator (for example, ellagic acid, kaolin or micronised silica) and calcium. Formation of Xase and prothrombinase complexes on the surface of the phospholipids enables prothrombin to be converted to thrombin, with subsequent clot formation. The result of this test is determined with reference to the time for clot formation. The APTT test is used to evaluate the intrinsic coagulation pathway, which includes factors I, II, V, VIII, IX, X, XI and XII, and is generally performed in a clinical laboratory.
A further test is the ACT (activated clotting time) test, which resembles the APTT test, but uses a sample of whole blood. Other useful tests have been developed, including immunochemical assays for activation peptide factor IXa, anti-thrombin, Protein C and Protein S.
In recognising the need for the provision of further tests which can be used to quickly and reliably determine levels of anti-coagulants in a blood sample, the present inventor, following extensive experimentation, has provided a device which has utility in the measurement of the viscosity and/or density of a fluid sample. The device can be used to determine blood clotting, and as such can be used to provide a quick and accurate determination of the levels of clotting factors, such as anti-coagulants in a blood sample.